Cover crop performance in dryland wheat production systems of the Pacific Northwest

Authors: BARROSO, JUDIT - Oregon State University; Adams, Curtis; Durfee, Nicole; SINGH, SURRENDRA - Oregon State University; HAGERTY, CHRISTINA - Oregon State University; MACHADO, STEPHEN - Oregon State University; GOURLIE, JENNIFER - Oregon State University; NAMDAR, GRAYSON - Oregon State University; OREJA, FERNANDO - Oregon State University; PRITCHETT, LARRY - Oregon State University; KRIETE, LINNEA - Oregon State University; CALDERON, FRANCISCO - Oregon State University; Reardon, Catherine

Submitted to: Crops and Soils
Publication Type: Trade Journal
Publication Acceptance Date: 10/23/2025
Publication Date: 10/23/2025
Citation: Barroso, J., Adams, C.B., Durfee, N.M., Singh, S., Hagerty, C.H., Machado, S., Gourlie, J.A., Namdar, G.F., Oreja, F.H., Pritchett, L., Kriete, L., Calderon, F.J., Reardon, C.L. 2025. Cover crop performance in dryland wheat production systems of the Pacific Northwest. Crops and Soils. 58(10):1-17 Available:https://www.researchgate.net/publication/396874959_Cover_crop_performance_in_dryland_wheat_production_systems_of_the_Pacific_Northwest

Interpretive Summary: Cover cropping, which is production of a crop for its ecological or cropping system benefits, has been extensively studied in certain regions and cropping systems. Growing cover crops during the conventional fallow phase of winter wheat-fallow systems of the semi-arid Pacific Northwest has been identified as an opportunity to build resilience and enhance farm profitability, though little research has been conducted in the region. In this research project, we evaluated both fall-plant and spring-planted cover crop species at two sites differing in rainfall over two years. Fall-planted cover crops generally produced more biomass than spring-planted covers, with winter peas and the fall species mix (winter barley, peas, and yellow mustard) being most productive. Spring-planted cover crops simply could not produce sufficient biomass given the agronomic and environmental dynamics of the region. Cover crop consumption of soil water is a major concern of wheat producers. Results showed, following a year of greater than average precipitation, no negative effects of cover crops on fall soil moisture at the higher precipitation site, though fall-planted cover crops reduced soil moisture at the lower precipitation site. Pending the results of studies evaluating wheat following cover crops, this is a potential concern to producers in the low rainfall zone. A potential benefit of cover crops is the suppression of weeds without herbicide use. The suppressive effect of cover crops on weeds ranged from null to moderate and fall-planted cover crops were the most effective. Importantly, fall-planted cover crops saved one herbicide application and so reduced herbicide pressure without exacerbating future weed issues as they were chemically terminated in mid-May before weeds set viable seeds. Overall, certain fall-planted cover crops showed promise to enhance ecosystem services during the traditional fallow period of regional wheat systems.

Technical Abstract: Cover cropping in the fallow phase of winter wheat-fallow systems of the semi-arid Pacific Northwest has been identified as an opportunity to build resilience and enhance farm profitability. Nine different cover crops were evaluated in 2021 and 2022 for biomass production and impacts on soil water and weed infestation at two sites, one in the intermediate precipitation zone (16.6 inches) and the other in the low precipitation zone (10.3 inches). Cover crop growth was dependent on location, year, planting timing, and species. Fall-sown cover crops generally produced more biomass than spring-sown cover crops, with winter peas and the fall species mix being most productive. Following a year of greater than average precipitation, no negative effects of cover crops on fall soil moisture were observed at the intermediate precipitation site, while fall-sown cover crops reduced soil moisture at the low precipitation site. The suppressive effect of cover crops on weeds ranged from null to moderate, with fall-sown cover crops more consistently suppressing weeds than spring-sown cover crops. Additionally, fall-sown cover crops saved one herbicide application and so reduced herbicide pressure without exacerbating future weed issues as they were terminated before weeds set viable seeds. Overall, certain fall-sown cover crops showed promise to enhance ecosystem services during the traditional fallow period.